In the first post, we looked at configuring an interactive shell session such that it retains infinite command history. The recommended setup looks like this:

HISTFILE="$HOME/.local/share/bash/history"
shopt -u histappend
HISTSIZE=-1
HISTFILESIZE=-1

See the post for all the details.

Ignoring specific commands

If we think of the command history as a list of commands that might be handy for reuse at some point, we probably don’t want absolutely everything in there. For example, ls and related commands are a) short and easy to write at any time without accessing history, and b) only useful in the context or working directory they were originally issued in, which we don’t really have available.

Another class of commands I never recall from history are those interacting with the history itself, such as history and fc.

In my dotfiles, I have aliases for cd .. and cd ../..; I don’t need those in history either.

And finally, I’m not interested in exit.

To specify which commands shouldn’t go into history, Bash provides the HISTIGNORE variable. It’s a colon-separated list of patterns, and commands matching the pattern (anchored at the beginning of the line) aren’t stored to history.

For example, for the commands described above as not interesting to me, I can set

HISTIGNORE='exit:history:l:l[1als]:lla:+(.)'

to ignore exit, history, most of my ls aliases¹, and commands consisting of any number of periods. +(.) is an extended glob pattern meaning “one or more periods”; HISTIGNORE understands extended globs if the extglob shell option is enabled, which by default it is in interactive shells.

The list is probably rather conservative and stores some commands I’m not interested in, but I’d rather have that than missing out on stuff I do want to see later on.

General history control settings

For more general control of what goes into history, Bash provides a variable HISTCONTROL. It is also colon-separated, with values taken from this list:

• ignorespace: ignore commands starting with a space character

  $ echo "Hello"
  Hello
  $  echo "Starts with blank"
  Starts with blank
  $ history | tail -n2
      6  echo "Hello"
      7  history | tail -n2

• ignoredups: don’t store commands that exactly match the last stored command

  $ echo 1
  1
  $ echo 2
  2
  $ echo 2
  2
  $ echo 3
  3
  $ history | tail -n4
      9  echo 1
     10  echo 2
     11  echo 3
     12  history | tail -n4

• ignoreboth is the same as ignorespace:ignoredups

  $ echo 1
  1
  $  echo "Start with blank"
  Start with blank
  $ echo 2
  2
  $ echo 2
  2
  $ history | tail -n3
     18  echo 1
     19  echo 2
     20  history | tail -n3

• erasedups removes all lines from history matching the current command before storing it

  $ echo 1
  1
  $ echo 2
  2
  $ history | tail -n3
     16  echo 1
     17  echo 2
     18  history | tail -n3
  $ echo 3
  3
  $ echo 2
  2
  $ history | tail -n5
     15  echo 1
     16  history | tail -n3
     17  echo 3
     18  echo 2
     19  history | tail -n5

I use HISTCONTROL='ignoreboth'; the only reason I’m not using 'ignoreboth:erasedups' is because sometimes, I want to repeat a sequence of commands from history using Ctrl+O (execute the current line from history and fetch the next one, operate-and-get-next), and erasedups might remove commands from the middle of such sequences.

Realistically, though, that’s a pretty unlikely edge case, and I might enable erasedups at some point. It would get rid of more than 7,500 commands in my history, apparently!

The setup so far

Taken all together, our history setup now provides infinite history, and only stores what we want:

# No clutter in the home directory
HISTFILE="$HOME/.local/share/bash/history"

# Overwrite when storing
shopt -u histappend

# Infinite session history
HISTSIZE=-1

# Infinite history file
HISTFILESIZE=-1

# Don't store commands that aren't useful in history
HISTIGNORE='exit:history:l:l[1als]:lla:+(.)'

# Ignore commands starting with space, and duplicates
HISTCONTROL='ignoreboth'

In the next post, we’ll examine how to get multi-line commands into history, and add timestamps to commands.